This invention relates to a round bar cutting tool for gear cutting and finishing operations, having a cutting end with at least two clearance faces and at least one cutting face, and with a shank having a generally round cross sectional configuration for clamping in a tool receiving bore of a cutter head by clamping means.
The invention further relates to a cutter head provided for holding such a round bar cutting tool, with a substantially disk-shaped cutter head body rotatable around a central axis. The cutter head body has at least one cutting tool receiving bore penetrating through it substantially in the direction of its thickness and serving to accommodate a round bar cutting tool. The cutter head body further has at least one clamping bore for accommodation of the clamping means. Starting from the outer periphery, the clamping bore penetrates the cutter head body in a substantially radial direction perpendicular to the cutting tool receiving bore, and intersects the cutting tool receiving bore.
A round bar cutting tool and a cutter head of this type originate from developmental work dating back to 1968, by the company Klingelnberg Sohne in Hueckeswagen, Germany, which are represented in FIG. 5 as known prior art. Before this prior art is dealt with in greater detail, the prior art that led up to the developmental work at that time will first be discussed.
In the so-called Oerlikon method of producing bevel gears, then as now bar cutting tools with shanks of rectangular cross-sectional configuration are used. Cutter heads with axial openings or slots of correspondingly rectangular cross-sectional configuration are provided for use with the bar cutting tools. One example of a bevel gear cutting machine of the applicant, on which sets of gears can be produced both according to the Oerlikon method and the so-called Gleason method (described below), is the SPIROMAT S 25, which is shown for instance in the Oerlikon company brochure S 25 Spiralkegelrad-Verzahnmaschine, OGT-S 25fD/hF. The cutter head required for the Oerlikon method is fitted with a plurality of cutting tool groups with three cutting tools each. Each group includes an outside cutter, an inside cutter and a rough cutter. Three faces must be reground on the cutting end of each Oerlikon bar cutter during sharpening. The cutters are mounted radially from the outside in slots open at the periphery of a cutter head body, with clamping or filler pieces added if necessary. A shrink ring is then placed around the cutter head body. This ring has clamping screws suitably arranged for clamping the cutting tools tight in their slots. The production of the axial peripheral slots in the cutter head body and the additionally required shrink ring with the clamping means of such a cutter head are costly and cumbersome. This was one of the reasons for the development of the round bar cutting tool and cutter head according to FIG. 5.
In the Gleason method (EP-B1 0 203 085), bar cutting tools of rectangular cross sectional configuration and with rectangular mounting surfaces are utilized, and are designed so that the rough cutter can be eliminated. A cutting tool group is therefore made up of only two bar cutters, meaning that a greater number of cutting tool groups can be provided in a cutter head. This enables faster gear cutting; however, the production of the cutter head and of the bar cutters is hardly simplified in this way. However, some simplification does arise from the fact that these known bar cutters are reground only on two faces in the direction of the shank during sharpening, so that the cutting face of these cutting tools can be provided with a coating that increases the life of the cutting tools. A coating of this type is known, for example, from U.S. Pat. No. 3,882,579.
The main problem with the cutter head comprised of a body with axial peripheral slots and of a shrink ring is especially the formation of the axial slots. The known cutter head according to FIG. 5 eliminates this problem, since round bar cutting tools can be mounted in cutting tool receiving bores which can be produced at less expense than angular slots, for example on jig boring and grinding machines. FIG. 5a shows a known round bar cutting tool cutter head 8' of this type which is fitted with five cutting tool groups, each containing three round bar cutters 10'. FIG. 5b shows this round bar cutting head cutter head 8' in the process of being fitted with the round bar cutters 10'. FIG. 5c shows a detail of the manner in which the round bar cutters 10' are mounted in the cutter head 8'. The round bar cutter 10' is inserted in an axial cutting tool bore 12'. Located in an axial bore 14 parallel thereto is an eccentric 16 that presses with its eccentric surface 17 against a circular-cylindrical clamping piece 18 that presses in turn against the circular-cylindrical shank of the round bar cutter 10.
To mount the bar cutter, first of all, the clamping piece 18 is pushed from the outside through an insertion bore 21 up to the cutting tool bore 12'. Subsequently, the eccentric 16 is inserted into the axial bore 14. The eccentric 16 has a square actuating dog 19 so that a wrench or the like can be used to rigidly clamp the clamping piece 18 to the round bar cutter 10' through the eccentric 16, thus rigidly clamping the bar cutter 10' in its axial cutter bore 12'. A gauge 20, shown in FIG. 5d, serves to position the round bar cutter 10'. The axial height of the round bar cutter 10' and the orientation of its cutting face are set with the gauge 20. The set-up of the round bar cutters 10' in this known cutter head is difficult, and the originally set orientation of the cutting face of the round bar cutter 10' can easily shift during use. As little as a corresponding load exerted on the cutting face of a round bar cutter 10' is sufficient to turn it slightly about its longitudinal axis. This can not be prevented with the cylindrical clamping piece 18, no matter how fast it is tightened. Furthermore, the round bar cutter 10' used in this known cutter head must also be reground on three faces during sharpening and, therefore, does not permit coating the cutting face to increase the serviceable life of the cutters. Moreover, cutting tool groups with three such round bar cutters 10' each must be used, thus limiting the number of round bar cutters 10' that can be accommodated in the cutter head 8'.